Edwards D P, Purpura K P, Kaplan E
Laboratory of Biophysics, Rockefeller University, New York, NY 10021, USA.
Vision Res. 1995 Jun;35(11):1501-23. doi: 10.1016/0042-6989(94)00253-i.
The striate cortex of macaque monkeys contains an array of patches which stain heavily for the enzyme cytochrome oxidase (CO blobs). Cells inside and outside these blobs are often described as belonging to two distinct populations or streams. In order to better understand the function of the CO blobs, we measured the contrast sensitivity and spatial frequency response of single neurons in and around the CO blobs. Density profiles of each blob were assessed using a new quantitative method, and correlations of local CO density with the physiology were noted. We found that the CO density dropped off gradually with distance from blob centers: in a typical blob the CO density dropped from 75% to 25% over 100 microns. Recordings were confined to cortical layers 2/3. Most neurons in these layers have poor contrast sensitivity, similar to that of the parvocellular neurons in the lateral geniculate nucleus. However, in a small proportion of layers 2/3 neurons we found higher contrast sensitivity, similar to that of the magnocellular neurons. These neurons were found to cluster near blob centers. This finding is consistent with (indirect) parvocellular input spread uniformly throughout layers 2/3, and (indirect) magnocellular input focused on CO blobs. We also measured spatial tuning curves for both single units and multiple unit activity. In agreement with other workers we found that the optimal spatial frequencies of cells near blob centers were low (median 2.8 c/deg), while the optimal frequencies of cells in the interblob regions were spread over a wide range of spatial frequencies. The high cut-off spatial frequency of multi-unit activity increased with distance from blob centers. We found no correlation between spatial bandwidth and distance from blob centers. All measured physiological properties varied gradually with distance from CO blob centers. This suggests that the view of blob cells subserving visual functions which are entirely distinct from non-blob cells may have to be reevaluated.
猕猴的纹状皮质包含一系列对细胞色素氧化酶（CO斑）染色很深的斑块。这些斑块内外的细胞通常被描述为属于两个不同的群体或信息流。为了更好地理解CO斑块的功能，我们测量了CO斑块内及其周围单个神经元的对比敏感度和空间频率响应。使用一种新的定量方法评估了每个斑块的密度分布，并记录了局部CO密度与生理学之间的相关性。我们发现，CO密度随着与斑块中心距离的增加而逐渐下降：在一个典型的斑块中，CO密度在100微米的距离内从75%下降到25%。记录限于皮质第2/3层。这些层中的大多数神经元对比敏感度较差，类似于外侧膝状核中的小细胞神经元。然而，在一小部分第2/3层神经元中，我们发现其对比敏感度较高，类似于大细胞神经元。这些神经元聚集在斑块中心附近。这一发现与（间接的）小细胞输入均匀分布在整个第2/3层以及（间接的）大细胞输入集中在CO斑块上的情况一致。我们还测量了单个单元和多个单元活动的空间调谐曲线。与其他研究者一致的是，我们发现斑块中心附近细胞的最佳空间频率较低（中位数为2.8周/度），而斑块间区域细胞的最佳频率分布在很宽的空间频率范围内。多单元活动的高截止空间频率随着与斑块中心距离的增加而增加。我们没有发现空间带宽与离斑块中心距离之间的相关性。所有测量的生理学特性都随着与CO斑块中心距离的增加而逐渐变化。这表明，认为斑块细胞执行与非斑块细胞完全不同的视觉功能的观点可能需要重新评估。
